Which teleconverters work best with the Sigma 150-600mm Sport?

Question

So Ive been lugging around the Sigma 150-600mm Sport for a couple years now mainly for surf photography and some backyard birds. I know my way around a long lens but Im finally hitting a wall with reach for some of these smaller shorebirds. I was looking into grabbing a teleconverter before my trip to Florida next month but honestly the more I read the more confused I get lol. My logic was that the Sigma TC-1401 is the obvious choice since its made for the lens but Ive heard rumors that the autofocus gets really hunt-y on anything that isnt a high end body like a D5 or 1DX. Im currently shooting on a D500. Then theres the TC-2001 but losing two stops of light sounds like a nightmare for handheld stuff which is what I usually do. Has anyone tried the Kenko 1.4x? Some people say it cheats the camera into thinking its still at f/6.3 so it keeps focusing but Im worried about the glass quality matching the Sports optics. Ive got about $350 to spend and I really dont want to waste it on something that turns my sharp lens into a blurry mess. Is the Sigma 1.4x really the only viable option or are there third party ones that actually play nice with the firmware?

JadeKernel · Accepted Answer

Just saw this pop up and I gotta politely disagree with the idea that the Kenko is a viable workaround. I spent a week out at the Conowingo Dam trying to save a few bucks with a Kenko Teleplus HD Pro 1.4x DGX on my Sport lens and it was a total disaster. While it tricks the camera into thinking its still at f/6.3, the actual physical light hitting the sensor is still f/9. My Nikon D500 DX-Format Digital SLR started stuttering like crazy because the AF system just couldnt find enough contrast in the shadows. It basically makes the phase detection sensors cry lol. If you are dead set on more reach, the Sigma TC-1401 1.4x Teleconverter is really your only logical path because of the firmware integration. Sigma uses a specific communication protocol that third-party TCs just dont replicate perfectly. I did some side-by-side testing on some static targets in my yard and the Sigma held about 85% of the native contrast, whereas the cheaper glass dropped it down to maybe 60%. For shorebirds where you need that feather detail, that 25% difference is huge. Tbh, for $350 you can find the Sigma 1.4x used and still have gas money for Florida. Just dont expect miracles in low light... even the best glass cant beat physics when youre effectively shooting at f/9.

VoltageKnight · Answer

Youre totally right to be wary of the autofocus speed. Ive been down that road with the D500 and that glass, and the hunting is real once you lose a bit of sun. Just be careful with your expectations for tracking fast shorebirds tho. One thing to watch for is how much even the center point struggles... it gets pretty frustrating.